Select the most appropriate option to fill in the blank.

Dozens of dogs in Norway have recently been hit by a mysterious and at times, ______ illness, raising concerns among dog owners.

fatal

The most appropriate option to fill in the blank is fatal.

The word "fatal" means causing death. It is the most appropriate word to use in this context, as it conveys the meaning of the illness being very serious and potentially deadly.

The other options are not as appropriate.

• Suspicious means arousing or deserving suspicion. This is not the right word to use, as it does not convey the same meaning as "fatal."
• Desperate means feeling or showing extreme sadness, anxiety, or despair. This is not the right word to use, as it does not convey the same meaning as "fatal."
• Dreary means dull and boring. This is not the right word to use, as it does not convey the same meaning as "fatal."